\(H_{\rm cond}\)  corresponds to two conduction bands (channels): one with symmetry \(3z^2-r^2\)  (\(\tau =1\) ) and another that takes into account the degenerate \(\pi \) -manifold \(xz,yz\)  (\(\tau =-1\) ) [1]}:
\(H_{\rm cond} = \sum _{k \tau \sigma }\varepsilon _{k \tau } {c}^\dagger _{k \tau \sigma }{c}_{k \tau \sigma };\) 
